Spirometer

Abstract

The chronic nature of asthma necessitates regular self-monitoring of respiratory function in susceptible individuals, however the available devices for performing the necessary measurements are either inaccurate or expensive and bulky. The present invention provides a small, cheap spirometer for efficient, accurate and convenient measurement of breathing characteristics.

The invention claimed is: 
     
       1. A spirometer for measuring throughput airflow comprising:
 a spirometer body having a cylindrical wall defining a cavity and having one or more windows arranged to admit ambient light to the cavity; 
 one or more deflectors configured to cause an airflow input to the cavity defined by the spirometer body to rotate; 
 a rotor arranged inside the cavity defined by the spirometer body to be caused to rotate responsive to the rotating airflow; and 
 one or more photodetectors, arranged at the wall of the spirometer body facing into the cavity to detect an amount of light incident thereon inside the cavity; 
 wherein the spirometer is configured such that, as an angle of the rotor changes as it rotates, the amount of the ambient light admitted to the cavity by the one or more windows and conveyed to the or each photodetector is varied due to obstruction by the rotor; and 
 wherein the one or more photodetectors form part of an electrical network configured to, in use, provide an electrical signal useable to detect the rotation rate of the rotor. 
 
     
     
       2. A spirometer as claimed in  claim 1 , wherein the electrical network is connected to one or more contacts of a phone plug that is coupled to, or rigidly connected to the spirometer. 
     
     
       3. A spirometer as claimed in  claim 1 , wherein the rotor comprises a vane portion rigidly connected to a shaft portion such that the vane portion can rotate about an axis defined by the shaft portion; and
 wherein both end portions of the shaft portion are pivotably mounted in respective sockets of the spirometer, such that the vane portion is mounted to rotate in the rotating airflow. 
 
     
     
       4. A spirometer as claimed in  claim 3 , wherein the one or more photodetectors are arranged partially around a periphery of a surface bounded by rotational edges of the vane portion. 
     
     
       5. A spirometer as claimed in  claim 4 , wherein the one or more photodetectors are located in recesses in the wall of the spirometer body facing into the cavity. 
     
     
       6. A spirometer as claimed in  claim 5 , wherein the cavity of the spirometer body defines a first radius and a radial extent of the vane portion defines a second radius; and wherein the second radius is such as to allow it to block light within the cavity from reaching the one or more photodetectors but less than the first radius allowing free rotation within the cavity. 
     
     
       7. A spirometer as claimed in  claim 6 , wherein an axial extent of the or each window is less than and contained within an axial extent of the rotor. 
     
     
       8. A spirometer as claimed in  claim 7 , wherein the axial extent of the rotor is substantially the same as an axial extent of the cavity. 
     
     
       9. A spirometer as claimed in  claim 1 , wherein the cylindrical wall comprises a single window and a single photodetector. 
     
     
       10. A spirometer as claimed in  claim 1 , wherein the cylindrical wall comprises a single window and a plurality of photodetectors. 
     
     
       11. A spirometer as claimed in  claim 10 , wherein the photodetectors in the plurality of photodetectors are spaced at angles around the cylindrical wall. 
     
     
       12. A spirometer as claimed in  claim 1 , wherein at least one of the one or more photodetectors is a photodiode. 
     
     
       13. A spirometer as claimed in  claim 1 , wherein the cylindrical wall of the spirometer is opaque except for the one or more windows arranged to admit ambient light to the cavity. 
     
     
       14. A spirometer as claimed in  claim 1 , wherein the spirometer is connected to an electronic device. 
     
     
       15. A spirometer as claimed in  claim 1 , wherein the light incident on the one or more photodetectors is not provided by active or powered light source. 
     
     
       16. A spirometer as claimed in  claim 1 , wherein the electrical network comprises one or more resistors. 
     
     
       17. A spirometer as claimed in  claim 16  wherein the one or more resistors are in the range 500 Ohm-3 k Ohm and in serial connection with the rotor. 
     
     
       18. A method of measuring throughput airflow using a spirometer as claimed in  claim 1 , comprising the steps of:
 a. connecting the spirometer to an electronic device; and 
 b. detecting, using the electronic device, the electrical signal provided by the spirometer experiencing the airflow therethrough; and 
 c. processing, using the electronic device, the electrical signal to obtain a measurement of a characteristic of the throughput airflow. 
 
     
     
       19. A method as claimed in  claim 18 , wherein processing, using the electronic device, the electrical signal comprises determining a rotation rate of the rotor from a component of the electrical signal produced by the operation of the one or more photodetectors as the rotor rotates. 
     
     
       20. A method of detecting throughput airflow as claimed in  claim 19 , wherein processing, using the electronic device, the electrical signal further comprises the step of performing a Discrete Fourier Transform (DFT) to convert a component of the electrical signal produced by the operation of the one or more photodetectors as the rotor rotates into a rotation rate. 
     
     
       21. A method as claimed in  claim 18 , wherein processing, using the electronic device, the electrical signal comprises determining characteristics of the airflow from a determined rotation rate of the rotor, based on calibration data defining relationships therebetween for the spirometer. 
     
     
       22. A method as claimed in  claim 18 , wherein processing, using the electronic device the electrical signal further comprises determining the direction of rotation of the rotor. 
     
     
       23. A method of manufacturing a spirometer, comprising:
 a. Providing a spirometer body having a cylindrical wall defining a cavity and having one or more windows arranged to admit ambient light to the cavity; 
 b. providing inlet and outlet deflectors configured to cause an input airflow to the cavity defined by the spirometer body to rotate and a rotor comprising a vane portion rigidly connected to a shaft portion; 
 c. providing one or more photodetectors arranged at the wall of the spirometer body facing into the cavity to detect an amount of light incident thereon inside the cavity; 
 d. forming part of an electrical network, coupled to the or each photodetector and configured to, in use, provide an electrical signal useable to detect the rotation rate of the rotor; 
 e. assembling the rotor between the inlet and outlet deflectors such that both end portions of the shaft portion are pivotably mounted in respective sockets defined at a radial center of the deflectors, such that the vane portion is mounted to rotate in the rotating airflow such that, in use as an angle of the rotor changes as it rotates the amount of the ambient light admitted to the cavity by the one or more windows and conveyed to the or each photodetector is varied due to obstruction by the rotor; and 
 f. coupling or rigidly connecting a phone plug to the spirometer and connecting the electrical network to one or more contacts of the phone plug that is coupled to or rigidly connected to the spirometer.